This is so hard, I love each one in their own way! It would have to be Deathly Hallows Part 1 at the moment (and I have a feeling in 2 weeks it will be part 2) but I also love Chamber of Secrets a lot!
OOtP and HBP were both amazing but could have been better. Philosophers Stone will always be special just because it's the first one. Goblet of Fire was great and Prisoner of Azkaban was one of the best also!
It's almost an impossible question, it's like choosing between your children!

After PoA came out, I was desperately hoping that Alfonso Cuarón would direct OotP (the book I had read more than any other), because he did such a wonderful job with PoA. However, that was not the case and I think that my connection with the OotP book made the movie the biggest disappointment of the franchise for me.

EDIT: I love looking back at the reactions to PoA. It almost always seems to fall into the top two spots or the bottom two. Rarely does it fall in the middle. Love it or hate it, right?

I'm one of those people who likes it when the movie is as close to the book as possible. So, I enjoy SS and CoS the best, but I think CoS is my favorite (though SS is a very close second). DH part 1 was pretty good. I'm excited for part 2 (though I work at a movie theater, so I have to work the midnight premier instead of watching it... Oh well)

I'm a little surprised that PoA has so many votes. That one was my least favorite, and many people I've talked to didn't like that one very much either... Oh well, I guess I'm outnumbered here

I'm a little surprised that PoA has so many votes. That one was my least favorite, and many people I've talked to didn't like that one very much either... Oh well, I guess I'm outnumbered here.

You're probably not outnumbered. From what I can tell, it seems to be pretty close to 50:50 in terms of those that love it and those that hate it. Very few fall in the middle. I am one of those that loves the movie but I understand completely why some don't. No judgments here!

It would be interesting, for me at least, to see where DH2 lands. I'm thinking, from all that I've seen and read, it will be higher than DH1 but whether it will land in #3, it very well could. No chance it will crack the top 2 though.

It's so difficult for me to actually go ahead and rate the movies. I loved all of them, and i feel so mean giving one of them the bottom spot. I'll just put it in a few thoughts about the movies!

Philosopher's Stone -

The sweetest movie the series has to offer. Daniel Radcliffe, Emma Watson, Rupert, Dumbledore and Hagrid did brilliantly to get the viewers to like their characters. The movie has warmth, and the magical vibe to it! Seen this movie about 20 times!

Chamber of Secrets -

Lovely. Didn't stray too far away from the first one, but did have some significant character development. I've seen this movie about a dozen times! The music in the first two movies was so magical.

Prisoner Of Azkaban -

I love this movie for several reasons. First, the trio, dumbledore and Lupin look the closest to how the character was intended to look in the book, and that was a great feat! Second, A brilliant story helped the movie, and David Thewlis was amazing as Lupin! Third, loved the change of musical style, for eg: when Marge's swelling up, a cheeky piece of Opera's playing the background, or when Lupin plays the record during the Bogart scene!

Goblet Of Fire/Order Of the Phoenix

I haven't rewatched these movies recently, and so i don't really remember how i felt about them. I would love rewatching these movies, just like any other HP movie. I remember GOF a little bit, and the begining of the friction between Trio was shown pretty well. I remember OOTP vaguely, and it has one of my favority lines from the series:
'If Voldemort's raising an army, I want to fight'

Half Blood Prince -

This one's tricky. I feel a person who has reread HBP novel, can really LOVE the movie. The movie's choice of scenes was great, considering they left out the depressing parts (which the book was full of). The dramatic/foggy/darkness vibe they had going on through the movie was spectacular. I liked how they replaced the constand bickering parts with more heart-warming scenes. The music was appropriate. The sectumsempra scene was pretty good. Also, I liked the scene where they burnt down the Burrow.

I have a really hard time ranking the movies because if I was going to solely judge them as movies, my list would be very different than if I rated them in comparison to the books.

Sorcerer's Stone/Philosopher's Stone

This one would be my number one pick and my favorite film of the series if I were to judge the films in comparison to the books. Because the novel is so short (in relation to the others) it was easy for the filmmakers to adapt it in a film that stayed true to almost every detail. And Richard Harris is Dumbledore, no one ever could have played that character better, it's a shame he passed away.

If I were to look at this one solely as a film and completely take the book from my mind (which is really hard), I would say this movie was decent. The special effects were great, the writing was pretty good, and the acting had its moments of greatness and its moments of weakness.

Chamber of Secrets

In comparison to the books, once again I believe they did a great job adapting this one into a film. Again, CoS was a fairly short book and therefore rather easy to keep the true essence of the story.

This was my second least favorite book in the series because I felt it was rather boring, so of course I felt the same way about the film. The acting had definitely improved amongst the young actors. I no longer felt as if Emma Watson thought she was on stage in a theater (over animating her movements and over enunciating her words). The special effects were still good and the writing still decent. A few cheesy moments, but at this point it was still a kids movie so that's understandable.

Prisoner of Azkaban

I know there were quite a few things wrong with this film. Since it's been a good 7 or 8 years since the last time I read it, I'm going to have a difficult time pointing out exactly what those things are. I remember when I first saw the film, I had just reread the book and I was angry about some of the things left out, especially the way it ended. And the time turner stuff, they barely explained that in the film.

That being said, now that I don't remember the book very well, it's probably up there as one of my favorite movies in the series. The writing definitely got worse and I hated the way they used Ron as stupid comic relief, but I loved the cinematography. As someone who is study cinematography in college currently, I have a great appreciation for this film. The scene when Harry is riding Buckbeak over the lake, is one of my favorites. I have to say though that I hated the way that from this film on they no longer really ever wore their uniforms and in this one in particular I was not a fan of the disheveled look that they were all sporting.

Goblet of Fire

Second worst film in the series in relation to the books. They left so much out. Again, it's been a while since I've read GoF, but I know I angry when I first watched the film. I feel like this is when they really started making major cuts on information they felt was unimportant. The problem was that they didn't know where the series was going and what was going to be important and I believe there are way too many scenes added that weren't in the book that were stupid filler scenes and they could have cut those and left in the important stuff. I really wish they hadn't cut the Dursley's from this film, that's one of my favorite scenes. And Dobby and Winky and S.P.E.W. I wish they'd left that in, I know it's not very important to the overall story line, but I liked it. Also, I don't really remember, but was there quidditch in this book? (I know there was the World Cup, but I mean at Hogwarts).

All that being said, the longer it's been since I've read the book, the more I love this film. Again, cinematically this film is brilliant. The shots when Harry is flying away from the dragon are beautifully shot. Just looking at the film itself, I'd say it's definitely in my top 3, maybe even number 1.

Order of the Phoenix

My least favorite film all around. I thought it was absolutely terrible in every respect. It did not stay true to the book in any way and it did not make coherent sense had you not read the book before hand. And it was WAY too short. Who ever said "let's take the longest book in the series and make it the shortest film" was a moron.

Half-Blood Prince

First off I cannot stand Michael Gambon. I don't think they could have done a worse job re-casting Dumbledore. He doesn't understand the character at all, but of course that's to be expected since he won't read the darn books. I think (aside from the scene in GoF where he chokes Harry and pins him against the wall) this is the worst film for Dumbledore. Dumbledore would never yell at the students the way he does in this one. He took the ignoring Harry thing in a whole different direction that just came off rude. I also was beyond upset about how much they left out of Tom Riddle's back story and all of the memories that Dumbledore showed Harry in the book. And let's not forget how little time was spent on the namesake of the book: Snape. They never explain why Snape is the the Half-Blood Prince or even really talk about it at all. Absolutely terrible.

As much as I hated it in relation to the novel, as a film itself I loved it. Again the cinematography was a step up, the writing definitely improved, there were far less cheesy moments, and at least it made sense. Just looking at it as film and not taking the book into account at all, HBP is one of my favorites.

Deathly Hallows, Part 1

In relation to the book I thought it was pretty good. They did a great job of making up for the mistakes they made in previous films. The decision to make it two films was great, they should have done that for every film starting with GoF. There were some things here and there that I wish they hadn't left out like the scene between Harry and the Dursleys. I don't know if you guys have seen that deleted scene, but I thought it was pretty well done I wish they hadn't cut it. When I read that part between Harry and Dudley it was honestly one of my favorite moments in the series.

I thought the film was a bit boring, but that's the risk they ran with making into two films. All the good stuff happens at the end, the first half of the book is pretty slow. But I'm glad it was slow and uneventful because that's how it's supposed to be. The cinematography, again, was phenomenal. The writing was finally better. We got less of angsty, whiny Harry that drove me crazy in OotP and HBP. They could have found a way to make the boring sections a little more interesting, but it was still pretty good.

Okay, so after that long rant (sorry guys, I just had so much to say haha) here are my lists. I had to make two, because they're just so different.

In order from favorite to least favorite based on how I liked them compared to the books:

1. SS/PS
2. CoS
3. DH, P1
4. PoA
5. GoF
6. HBP
7. OotP

In order from favorite to least favorite looking at them as just a film:

Now that all eight are released I can give an honest answer to this thread...

Deathly Hallows Part 1 will have to be my favorite. I never thought they would make another HP movie that was as in tune with the book as Prisoner of Azkaban was, but DH1 did it. Neither of those movies were as close to the plot of the book as the SS and CoS, obviously, but watching DH1 I really feel like I'm watching the book brought to life. I honestly don't find the camping scenes dull at all, just as I didn't find those chapters of the book dull. They were excellent, IMO, for a few reasons: 1. They build up slowly, from Ron's initial impatience, to his sullen looks at Harry and Hermione, and then finally to his explosion. The argument between Harry and Ron is important, because Ron voices concerns that many viewers surely will connect with- maybe Harry doesn't know what he's doing. This mistrust of Harry is something not seen too much in the first six films, because we are trained to believe Harry, through Dumbledore's guidance, is always on the right path. This changes around the middle of DH1. 2. I love the radio broadcast playing as they travel from site to site. One of my favorite scenes of the movie. The broadcaster saying "Thankfully the list is short," and then proceeding to list a couple dozen names, gets me every time. Voldemort is at large, and nowhere is safe. It's clear now just how much danger everyone is in. I love it. 3. Everyone else will hate it, but I also thought the dancing scene was fantastic. It's just like the wedding: everything is at its absolute worst, so it seems amazing that something so normal can still happen. It's amazing that two best friends can just dance together, given the situation they're in. Harry does his best to pretend with Hermione, at least for a few minutes, that everything is normal again. Reality hits her soon enough, but I think it was a good, lighter moment in a very dark film.

Another thing which stood out for DH1 was its score. The score for Part 2 was amazing as well, I thought, but in Part 1 it was so good that at times you hardly noticed it was there because the music fit in so well with the theme. The scene where Snape walks up the path to Malfoy Manor was one of my favorite scenes of the movie, largely because of the music. No one could have possibly hoped to equal the iconic themes of John Williams, but Desplat made two very memorable scores as well.

Finally, I liked the lack of exposition in DH1. It seemed nearly nonexistent, which IMO it should be seven movies in. They felt the need for a lot of recap in Part 2, which I found strange. They dive straight into the plot of this movie, without dwelling on the last one. It wasn't as though they made it impossible for non-readers to understand, it was just assumed that you had seen all the previous films (the only way the movie would have made no sense is if you had read none of the books and seen none of the movies. If that's the case, then, well)...

First off I cannot stand Michael Gambon. I don't think they could have done a worse job re-casting Dumbledore. He doesn't understand the character at all, but of course that's to be expected since he won't read the darn books. I think (aside from the scene in GoF where he chokes Harry and pins him against the wall) this is the worst film for Dumbledore. Dumbledore would never yell at the students the way he does in this one.

I don't recall Gambon's Dumbledore engaging in a lot of yelling in HBP. I recall him doing this in GoF. In fact, I recall a lot of characters talking at the top of their voice in GoF. Which is why it is my least favorite HP movie.

1. DH2- Above and beyond the greatest in the series in my opinion. I would rank it among the top 10 greatest films that I've ever seen in my lifetime.

2. SS- Everything about this film was just excellent. Perfect casting and legitimately had a 'magical' feel to it (which is something I felt was lost in the later films).

3. OoTP- People hate this film because it was short, but I thought they did a good job regardless (better than they did with GoF at least, IMO). The reason why I would place this movie 3rd in my list is because of Luna; they could NOT have picked a better girl to play that part.

4. DH1- Very close to the book (from what I remember). But I wouldn't place it above the ones I have already mentioned.

5. HBP- Still good, but meh. As someone else said, never really did get used to Gambon as the new Dumbledore....

6. GoF- Very disappointed they didn't make this one longer. It was my second favorite book (after DH), and so much was left out (not to mention the pace was blindingly quick). Also did not like the way they made Voldemort look. He needed a nose!!!!

7. PoA- Did not like the fact that the dementors strongely resembled LOTR's ringwraiths. Did not like the actor they casted for Sirius (especially with that beard & moustashe; made him look like a creeper, lol). However, I did like the actor they casted for Lupin. And then there was problem with the time traveling thing, which I always viewed a kind of plothole (but of course, this has to do more with the book than the movie).

8. CoS- Something about a 12 year old boy being able to fight and kill a massive snake with a sword irked me. Even in the magical world, something like this should not be possible. This bugged me in the book as well.

All in all, I really enjoyed all the movies. If I was looking for something to watch on the television and happened to see one of these (including CoS), I would not mind sitting down to watch it again. It's just that if I had to rank them, this is how I would do so and why.

For me Harry Potter and the Deathly Hallows part 1 and part 2 are the same movie, so it is my favorite in the series. Although SS in really close because its the one that started it all and I felt the magic lol.